Seed germination and plant growth are fundamental biological processes of great scientific, educational and commercial interest. Parents and teachers often wish to present plant growth to children and students, respectively, in a way that is both informative and dynamic, allowing observations of growth and development over time. However, whereas the growth of the shoot, i.e., the aerial portions of the plant (leaves, flowers and fruits), can be directly observed, the germinating seed, as well as the developing root system, which is often as extensive as that of the shoot system, are usually buried in the soil. Weier, T. E., et al., Botany: An Introduction to Plant Biology, 6th Ed. John Wiley & Sons, Inc., pp. 158-76. Thus, seed germination and the developing root system are typically obscured.
Plants can be grown aseptically in tissue culture. The practice of growing plants and plant tissues on defined media in closed containers is well-developed. See, for example, Dixon, R. A. (ed), Plant Cell Culture: A Practical Approach, IRL Press, Oxford, Washington D.C. (1985). Plant tissue culture is typically carried out either in a liquid culture medium or on a solid culture medium solidified with a gelling agent, e.g., agar or gellan gum. In both liquid and solid culture, seed germination and the growth and development of shoots and roots can be directly observed. However, liquid culture typically requires constant agitation, for example, on a mechanical shaker, to maintain an adequate level of dissolved gases in the medium. Dixon, supra; Biondi and Thorpe, "Requirements for a Tissue Culture Facility" in: Plant Tissue Culture: Methods and Applications in Agriculture, Thorpe, T. A. (ed) Academic Press, (1981), pp. 1-20. Thus liquid culture is not well-suited for observation of plant growth in the home or in many educational, industrial or commercial situations.
The growth of plants on solid culture medium allows for the direct observation of seed germination and the growth and development of the whole plant, including the root system, since gelling agents, such as agar and gellan gum, are typically transparent. However, gelling agents are also colorless and, therefore, are not particularly attractive to children, nor do they provide an ability to color-code plant cultures.
Dyes have been incorporated into culture media for physiological studies. Gollany, H. T. and Schumacher, T. E., Plant and Soil, 154: 151-59 (1993), describe the use of a pH-sensitive indicator dye, bromocresol purple, in agar medium to detect variations in pH along the length of the root.
Dyes, however, are often toxic or otherwise inhibitory to seed germination and plant growth, and so their general use in culture media is problematic. There are no reports of the incorporation of dyes into solid plant culture media in concentrations that impart a visible color to the culture medium and which permit seed germination. Furthermore, there are no reports of the use of such dyes to increase the attractiveness of aseptically cultured plants to children or for the color-coding of plant cultures for educational, research, industrial or commercial purposes.